The present disclosure relates to a charge applying member configured to apply an electric charge to a member to be charged for use in an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction peripheral having these functions, and an image forming apparatus with the charge applying member.
The image forming apparatus involves previously charging a photoconductor serving as an image carrier to a predetermined potential before forming an electrostatic latent image on the photoconductor. An example of a known charging device capable of charging the surface of the photoconductor is a contact type charging device which includes: a charging member including a conductive roller and a shaft passing through the axis of the conductive roller and having electric conductivity; a pair of bearings journaling both ends of the shaft; and a feeder member making contact with one end of the shaft and capable of applying a voltage to the conductive roller. The conductive roller has an elastic layer formed on the surface thereof and the voltage can be applied to the elastic layer. In the case of using the contact type charging device, the charging member and the photoconductor rotate relative to each other with the charging member held in contact with the photoconductor, so that the charging device applies an electric charge to the photoconductor.
If in this charging device rust forms at sliding interfaces between the shaft and the bearings or a contact site between the shaft and the feeder member, this may cause rotation failure or electric feeding failure, resulting in charging failure. For example, if a paper sheet is heated in order to fix a toner image transferred to the paper sheet and water contained in the paper sheet is evaporated in the charging device by the heating, so that the humidity inside the charging device is increased or if the charging member is exposed to high humidity for long periods, water may penetrate the conductive roller. Conductive rollers are usually made of a special material containing, for example, a highly acidic substance. Water having penetrated the conductive roller may force the highly acidic substance in the conductive roller to ooze out of it and the highly acidic substance may adhere to the surface of the shaft. If a highly acidic substance adheres to the shaft, rust will form on a contact portion of the shaft with the conductive roller, in which case it is difficult to stop the rust from developing from the contact portion with the conductive roller to sliding portions of the shaft with the bearings and a contact site of the shaft with the feeder member.
Relevant techniques for reducing charging failure due to rusting are known. In an example of the known techniques, a charging member includes a conductive roller and a shaft inserted into and through the conductive roller, wherein a rust inhibitor is applied to portions of the shaft facing both ends of the conductive roller. With this structure, even if rust forms on a portion of the shaft in contact with the conductive roller, the rust inhibitor makes the rust less likely to develop to the sliding portions with the bearings and the contact site with the feeder member.